The invention relates to a common rail system for internal combustion engines, having a high-pressure pump mounted on a part of the engine, especially on an engine block, control gear or reduction gear.
Mounting the high-pressure pump on the face end on the engine block below the cylinder head offers the advantage that shear forces from the drive mechanism are absorbed by the stable engine block. This also makes for a compact structure. Furthermore, the entire engine block can be used for both Diesel and Otto engines. No additional mounting brackets are needed. As needed, the lubrication of the drive can be integrated with the engine oil loop.
However, mounting the high-pressure pump on a part of the engine also involves problems. In the context of the present invention, it has been discovered that the temperature problem that exists anyway in common rail systems, resulting from the diversion in leakage of high-pressure Diesel fuel, is made even worse by mounting on the engine. Both measurements and simulation calculations have shown that the high-pressure pump becomes heated directly by the engine block and when mounted stationary virtually assumes the same temperature. In addition, heating of the high-pressure pump occurs from the lubrication of the drive mechanism with the hot motor oil. On the other hand, the fuel flow, used for cooling and lubrication, through the crank chamber of the high-pressure pump causes a major convective dissipation of heat from the engine. The heat flow taken from the engine is stored in the fuel and definitively contributes to heating of the fuel, which is undesirable especially in the tank. An expensive fuel cooler is therefore often needed in the low-pressure feed loop.
It is an object of the invention to furnish suitable structural provisions for thermally decoupling the high-pressure pump from the engine. No change is intended in the mounting position on the engine block, control gear or reduction gear.
In a common rail system for internal combustion engines, having a high-pressure pump mounted on a part of the engine, especially on an engine block, control gear or reduction gear, is attained in that the contact areas between the part of the engine and the high-pressure pump are minimized. This offers the advantage that the fuel cooler required can be made smaller, or in combination with a quantity-controlled high-pressure pump can possibly be dispensed with entirely. Both options offer a cost advantage over earlier concepts and thus have a competitive advantage.
A particular embodiment of the invention is characterized in that the number and area of air gaps between the high-pressure pump and/or the part of the engine is maximized. As a result, the quantity of heat transmitted by the engine to the high-pressure pump and thus into the fuel loop is reduced.
Another particular embodiment of the invention is characterized in that the mounting face on the part of the engine or on the high-pressure pump has a centering rib. The centering is required to enable a transmission of force to the drive shaft of the high-pressure pump. Achieving the centering by means of the centering rib has the advantage that the contact area absolutely required for the centering is minimized.
A further special embodiment of the invention is characterized in that the mounting face on the high-pressure pump is shielded by a cover plate. Such a cover plate is especially advantageous whenever the mounting area is relatively large and comes into contact with hot motor oil. By means of the cover plate, the heat transfer by convection is sharply restricted.
Another special embodiment of the invention is characterized in that the cover plate rests on an annular bearing face of the high-pressure pump. The annular bearing face offers stable support for the cover plate. At the same time, however, because of the annular embodiment of the bearing face, it is assured that the contact area between the cover plate and the high-pressure pump is minimized.
Another special embodiment of the invention is characterized in that a void is formed between the part of the engine or of the gear and the high-pressure pump. The void, which as a rule is filled with air, assures very good thermal insulation between the part of the engine and the high-pressure pump. This reduces the quantity of heat transmitted from the motor to the high-pressure pump still further.
Another special feature of the invention is characterized in that an insulating layer is introduced on the contact faces between the part of the engine and the high-pressure pump. The insulating layer comprises a material of low thermal conductivity. The insulating layer can already be applied in the process of production of the engine or high-pressure pump.
Further advantages, characteristics and details of the invention will become apparent from the ensuing description, in which various exemplary embodiments of the invention are described in detail in conjunction with the drawings. Characteristics recited in the claims and in the description can each be essential to the invention individually or in any arbitrary combination.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings.